2.1 Which effects can be expected of long-term exposure to levels of NO2 observed currently in Europe?

2.1.1
"The epidemiological studies provide some evidence that
long-term NO2exposure may decrease
lung function and increase
the risk of respiratory symptoms."
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2.1.2
"Methodological limitations constrain identification of
harvesting [(the advancement of mortality by only relatively few
days)] due to NO2 itself. The few [available]
long-term studies have not shown evidence for association
between NO2 and mortality. Associations have been
observed between NO2 and mortality in daily
time-series studies, but on
the basis of present evidence these cannot be attributed to
NO2 itself with reasonable certainty."
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2.2 Is NO2 per se responsible for effects on health?

For the effects observed in epidemiological studies, a clear
answer to the question cannot be given. Effects estimated for NO2exposure in epidemiological
studies may reflect other, often unmeasured, traffic related
pollutants, for which NO2 is an indicator.
Additionally, there are complex interrelationships among the
concentrations of
NO2, PM, and
ozone in
ambient air.
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2.3 Are health effects of NO2 influenced by the presence of other air pollutants?

WHO states:
"There have been few controlled human exposure studies
on interactions with other chemical pollutants, although several
studies show that NO2 exposure enhances [allergic]
responses [of asthmatics] to inhaled pollens. Some
epidemiological studies have explored statistical interactions
of NO2 with other pollutants, including
particles, but the findings
are not readily interpretable."
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2.4 Which characteristics of individuals may influence how Nitrogen Dioxide affects their health?

Are effects of NO2 dependent upon the subjects’ characteristics such as age, gender, underlying disease, smoking status, atopy, education etc?

What are the critical characteristics?

WHO states: "In
general, individuals with
asthma are expected to be
more responsive to short-term
exposure to inhaled agents,
when compared to individuals without asthma.
Controlled human exposure studies
of short-term responses of persons with and without asthma to
NO2 have not been carried out. There is limited
evidence from epidemiological studies that individuals with
asthma show steeper concentration-response relationships.
Small-scale human exposure studies have not shown consistent
effects of NO2 exposure on airways reactivity in
persons with asthma, even at exposure levels higher than typical ambientconcentrations. As for other
pollutants, children can reasonably be considered to be at
increased risk. There is limited evidence for influence of the
other listed factors [such as gender, smoking status,
atopy, education, etc.] on
the effects of NO2."
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2.5 Is there a threshold below which nobody’s health is affected by NO2?

WHO states: "The
evidence is not adequate to establish a
threshold for either short
or long-term [NO2]
exposure. While a number of
epidemiological studies have described concentration-response
relationships between
ambient NO2 and
a range of health outcomes, there is no evidence for a threshold
for NO2."